Our research objective remains the development of artificial lungs and artificial kidneys based on the membrane separation principle. A second generation of mass transfer devices is now emerging in part because of the availability of new materials, in part because of growing sophistication in the design and prediction of performance of mass transfer devices. In the next years, our program will involve: a) continuing theoretical studies of the determinants of gas transfer in blood oxygenators; b) further development of the microporous, flat sheet type of oxygenator, with special attention to water vapor change, control of microporosity of exchange membranes, interaction between blood and microporous materials, and factors of decay in gas transfer performance; c) further design of the microporous coiled tube oxygenator design, with special attention to the induction of secondary flows to achieve high oxygen transfer coefficients with a minimum resistance to blood flow; d) miniaturization of the microporous coiled tube oxygenator and development of branching and manifolding techniques that will permit the construction of an implantable membrane oxygenator; e) further theoretical and experimental study of some factors leading to platelet agglutination and aggregation in flow systems; f) application of the engineering exchanger theory, as it pertains to blood oxygenators, to the design and performance of the natural lung with a view to define design parameters of importance for implantable, artificial lungs.